In recent years, progress has been made in research and development of diverse functional devices which involve use of an organic semiconductor.
One typical example of such functional devices is an organic EL device. The organic EL element, which is a current-driven light-emitting element, includes a pair of electrodes, i.e. an anode and a cathode, and a functional layer layered between the pair of electrodes, the functional layer containing an organic material. The functional layer includes layers such as an organic light-emitting layer and a buffer layer. Further, there are cases where a hole injection layer is disposed between the functional layer and the anode. The hole injection layer is disposed for injecting holes to the functional layer. To drive the organic EL element, voltage is applied across the pair of electrodes to use the phenomenon of electroluminescence that occurs when holes injected from the anode into the functional layer recombine with electrons injected from the cathode into the functional layer. Given the high visibility of organic EL elements resulting from their self-luminescence, as well as their excellent shock resistance resulting from the solid-state structure thereof, more attention is now being given to the application of organic EL elements as a light emitter for various display devices or as a light source.
Organic EL elements can be largely divided into two types, according to the material used for forming the functional layer therein. The first type of organic EL elements is a vapor deposition type. A vapor deposition-type organic EL element has a functional layer that is mainly composed of low molecular material and that is formed as a film by applying a vacuum process such as a vapor deposition method. The second type of organic EL elements is an application type. In an application-type organic EL element, ink containing organic high molecular material or organic low molecular material having excellent thin film forming characteristics is applied, dried and formed into a film by a wet process such as an inkjet method and a gravure printing method.
Now, attempts are being made to realize large-sized organic EL panels by using application-type organic EL elements. As mentioned above, in application-type organic EL elements, the functional layer is formed by applying ink containing prescribed materials. When a wet process is adopted, the precision with which the application of functional layer material of the respective colors to corresponding positions on the substrate is performed is not influenced by the size of the substrate. Hence, the technical barrier to be overcome in realizing the manufacturing of large organic EL panels is relatively low.